Rotary drills to date have used largely the rotary stem principle with a rotary drill at the end of a stem extended to the face of the well being drilled. Another type of rotary drill has been the use of the stem but without rotating it. Rather than rotating the stem there has been the practice of forcing mud down through the stem to turn a mud motor which drills at the bottom. The chips, or cuttings, are circulated back up the outside of the stem. In the rotary stem approach mud is also used to carry the chips up the outside of the stem after the mud is forced down through the center of the stem. The mud also acts as a coolant in both cases.
In both of these practices the time and cost of changing bits by bringing up the drill stem piece-by-piece and then putting it back in after changing the bit in the reverse piece-by-piece process is immense. Ordinarily it consumes approximately 90% of the time, ranging from 50% up to 98%, depending on the depth of the well. The deeper the well, the higher percentage of time it takes to change bits. Time, of course, is cost because it is both labor and equipment being utilized over a period of time.
The costs of preparing, supplying and processing the mud as it is used are also extremely expensive. The cost of power to turn the drill is extremely high also, owing to the friction of the mud and the extremely heavy drill stem.
Only about 10% of power actually used in the drilling process is required for the cutting action separate and apart from other power requirements of turning the drill stem. This is not diminished appreciably by the mud power motor drill because of the high friction of mud being pressured in and out of the drill stem. Cable drilling that has been practiced to date is a bounce power system. The bit at the bottom of the well is bounced to give a jack-hammer effect with non-cutting rotation. This is a good drilling system for some purposes, but it is highly ineffective for deep drilling.
The instant invention utilizes a cable but in a far different manner. It is utilized as a method of suspending a power system rather than a method of moving a drilling mechanism directly. The cable is a conveyance means rather than a power transfer means in this invention.
Objects and distinguishing features of this invention are that it provides a method of changing bits that consumes no more than 10% of the time and as little as 2% of the time of present drill stem drilling systems, whether they are rotary drill stem or mud drilling motor systems. It provides a total rig cost system that is approximately 10% or less of present rig equipment cost systems for equal depth capacity. It provides a drilling system which requires less than one third the labor cost per time of drilling, thus making the total labor cost average between 3-10% of present labor drilling costs.
Another objective is to provide a means of drilling without changing hole diameters throughout an entire 25,000 feet or more of well drilling. The outset and the final hole diameter can be approximately eight inches for optimum drilling to any depth.
Another object is to provide a casing system with a capability of being used only at the strata where casing is needed rather than at entire hole lengths or depths just to case certain required sections.
Another objective is to provide a drilling system that can be portable on a truck for drilling up to 25,000 feet with the equipment carried on one semi-trailer truck.
Another objective is to provide a system that allows drilling from the ocean bottom or from the surface of the ocean with the same proportional advantages over present offshore or ocean drilling as the portable semi-trailer rig has over the land drilling conventional systems.